A hydrogel is a network of hydrophilic polymer chains in which water is the dispersion medium. The hydrogel is not dissolved but swelled in water so that it can contain a large amount of water in the structure thereof and thus it possesses a degree of flexibility very similar to that of natural tissue.
The hydrogel has been used in the medical and pharmaceutical field, such as the fields of tissue engineering, cell culture, sustained-release drug delivery systems, biosensors, soft lenses, medical electrodes, and the like, due to its unique hydrophilicity and flexibility, and has also been applied in various fields including absorbents for hygienic goods, delivery media of cosmetic agents, and the like.
As the conventional technologies using the hydrogel, Patent Document 1 (Korean Laid-Open Patent Publication No. 10-2014-0108803) discloses a method of preparing a hydrogel film, which includes preparing a resin for a hydrogel; forming a hydrogel by applying the resin for a hydrogel onto a surface of a release film and then drying the same; and crosslinking and swelling the hydrogel by infiltrating the hydrogel formed on the surface of a release film with a crosslinking-swelling agent. In this case, the resin for a hydrogel includes 1 to 40 wt % of a polymer resin containing one or more selected from a water-soluble polymer and a natural polymer, 0.05 to 20 wt % of sodium alginate, 0.1 to 20 wt % of a plasticizer, 0.1 to 20 wt % of a moisturizer, and 20 to 98 wt % of distilled water. Regarding Patent Document 1, it is described that a hydrogel film having excellent mechanical strength, good flexibility, excellent adhesion to skin, excellent comfort, and the like may be provided.
In addition, Patent Document 2 (Korean Registered Patent No. 10-1563325) discloses a method of preparing an antipyretic patch, which includes applying an adhesive onto one surface of an urethane film and then adhering a nonwoven fabric thereto; mixing a hydrogel with a functional material having antipyretic efficacy to prepare a functional hydrogel; applying the functional hydrogel onto a surface of the nonwoven fabric or one surface of a release film and then bringing the functional hydrogel in close contact with the nonwoven fabric or the release film in such a way that the functional hydrogel is positioned between the nonwoven fabric and the release film to prepare a patch sheet; thermally treating and drying the patch sheet to form a semisolid-phase functional hydrogel from the functional hydrogel; and cutting the patch sheet including the semisolid-phase functional hydrogel into a shape conforming with an application site of the human body. In this case, the hydrogel includes 5 to 15 wt % of polyacrylic acid, 10 to 40 wt % of glycerin, 1 to 10 wt % of sodium hydroxide, 0.1 to 3 wt % of agar, 0.1 to 3 wt % of Polysorbate 60, and water as the remainder, and the functional material is prepared by mixing a functional mixture comprising any one of menthoxypropanediol, menthyl lactate and mixture thereof; and oriental plant extracts comprising two or more selected from a cucumber extract, an aloe extract, a Tricholoma matsutake extract, a Phellodendron amurense bark extract, a carrot root extract, and a Lycium chinense fruit extract. The hydrogel and the functional material are mixed in a ratio of 97 to 99 wt % and 1 to 3 wt %, respectively. Patent Document 2 describes that when the antipyretic patch prepared by the above method is applied to a corresponding site in the human body, fever may be effectively reduced.
However, when a functional component is applied to a hydrogel as prior-art documents, the concentration of an active ingredient may be diluted or the stability of an active ingredient may be adversely affected within the shelf life of a product. For example, since the hydrogel has a high moisture content, decomposition caused by proliferation of microorganisms may occur, and high distribution costs are also required.